How many seasons of "All in the Family" were #1 in TV viewership?

Norman Lear had the audacity to put Archie Bunker on television in 1971, and America went absolutely crazy for this bigoted, politically incorrect loudmouth from Queens. "All in the Family" was so controversial that CBS ran disclaimers before episodes, but viewers couldn't get enough. How many consecutive seasons did this boundary-pushing sitcom hold the #1 spot in television viewership?